Structural Characterization and Antioxidant Activity Evaluation of Lignins from Rice Husk

Abstract

In recent years, lignin and extractives from herbaceous plants and crops are receiving increasing attention for their renewability and large annual biomass stock. It is worth noting that only a few studies deal with the chemical characterization of rice husk, a side product of one of the most important crops with regard to human nutrition. Thus, in this study lignin from rice husk was isolated and characterized. Two different extraction procedures were optimized and tested: acidolysis and alkaline enzymatic (AE). The different lignins isolated were fully characterized by means of gravimetric, chromatographic (GPC), and spectroscopic (31P NMR, 2D-HSQC-NMR) analyses with the aim to compare yields, sample purity, and chemical properties, recognized as key parameters for future development. Notwithstanding the extraction procedure, the results highlighted that rice husk lignin is mainly formed by guaiacyl and p-hydroxyphenyl units. The acidolytic approach showed an appreciable lignin recovery and high purity, whereas the AE lignin sample was found to be rich in residual polysaccharides and oxidized functionalities. Moreover, different rice husk extracts, along with acidolysis lignin and AE lignin specimens, were assayed for their antioxidant activity by means of a DPPH radical scavenging test.

By-products of Rice Processing: An Overview of Health Benefits and Applications

“…The fibres found in rice husks are mainly lignin, hemicellulose, cellulose and hydrated silica [44]. These components are similar to those in ground rice husk made from defatted concentrated rice bran ( Table 4).…”

Selective Primary Alcohol Oxidation of Lignin Streams from Butanol‐Pretreated Agricultural Waste Biomass

“…Among these, rice is one of the most cultivated crops in the world with around 680 million tons produced per annum . Rice husks make up around 20 wt % of the rice grain and are composed of approximately 22 % lignin, 38 % cellulose, 18 % hemicelluloses, 2 % extractives, and 20 % ashes with variations depending on geographical origin . As a result of high lignin and ash content, the husks are not a viable animal feed, but they can be burnt to yield large quantities of silica that can be used in a number of material applications .…”

Antioxidant activities of lignin extracted from sugarcane bagasse via different chemical procedures

“…Many literatures have reported lignin extracted from corn stover [7], hybrid poplar [8], apple tree [9], green tea [10], rice husk [11], and black liquor [12], etc. for applications as antioxidants.…”